It is known that plasmas are gases ionized at very high temperatures, of the order of several thousands of degrees. It has already been proposed to use them in industry for making blowtorches notably for carrying out surface treatments.
A plasma can be obtained by the energization, through an electric field, of a gas enclosure, such as the inside a tube.
A plasma blowtorch is also known in which an electric field is generated by using an inductance surrounding a tube in which circulates a gas flow to be energized and which is supplied with a high frequency or ultra-high frequency alternating current of the order of 20 to 50 MHz. The inductance encompasses a tube made of an insulating material such as glass, inside which is formed a plasma. The formation of plasma inside a tube limits, however, the use of said blowtorches to the treatment of parts of reduced dimensions which can be introduced inside the tube. The low value of the energy density of the plasma obtained limits also the field of application of this blowtorch. Finally, the tube has the disadvantage of being fragile and costly.
Plasmas of higher energy density can be obtained at the outlet of a metallic tube by using electric arc blowtorches which is generated an electric field radially between a central cathode placed inside the tube and the tube itself which forms an anode for creating an electric arc which is blowed by the gas to be ionized towards the outlet of the tube. However, this blowtorch has disadvantages which limit its applications; in particular, the plasma thus produced contains unavoidably impurities from the electrodes and these impurities may be undesirable for a surface treatment. Moreover, the operating costs of said blowtorches are high since the electrodes deteriorate rapidly and the gas flow is high.